The present invention relates to methods and apparatus for setting the operating mode of an integrated circuit which performs different functions in accordance with the operating mode selected.
Integrated circuits that are able to perform different functions are becoming more and more usual. Equipment in which an integrated circuit shall be included is often required to be compact and effective with respect to current consumption. Such requirements can be met by incorporating parts of the equipment in the integrated circuit. The more functions that are built into the integrated circuits, the larger the circuits. Furthermore, it is often beneficial to use one and the same circuit in different applications in which the circuit performs different working functions. In order for the circuit to operate, it is necessary to be able to set the circuit to different operating modes.
Earlier solutions to setting such circuits in respective operating modes have involved dedicating a number of circuit-mounted setting signal inputs to solely control setting of the circuit. A signal level is applied to these inputs, by applying to the inputs either a low or a high signal level, for instance signal earth or an operational voltage respectively, e.g. with the aid of a switch. The applied signal level is read into the circuit at a predetermined time point, normally when starting-up, and is there interpreted as an operating mode.
In a development of the aforedescribed method resulting in the ability to use the signal connections in normal operations subsequent to said connection having served as setting signal inputs, the signal connections are coupled to the earlier mentioned signal levels through the medium of resistors. This enables the signal connections to be used also in the normal operation that follows termination of the setting process without risking short circuiting.
The problem with these solutions is that it is necessary to dedicate a plurality of signal connections, and therewith a number of connecor pins, solely to the setting functions. The space available for accommodating electronics in modern equipment can be very limited, meaning that the larger the number of connector pins required by a circuit the more difficult it becomes to meet the requirement of compact equipment.
With regard to resistor-loaded setting signal inputs, a further problem resides in the fact that when the circuit transmits or receives signals on said signal pins upon completion of a mode setting process, current will flow through the resistors with increased power consumption as a result. This results, for instance, in the inability to meet the requirement of equipment compactness, particularly in those cases when the equipment is powered by a space-consuming battery.
U.S. Pat. No. 4,902,917 teaches a way of at least partially avoiding these problems. In this case, an integrated circuit is set to its operating mode by sending one of at least two different setting signals to a setting signal input. The different setting signals are obtained from clock signal outputs on the integrated circuit. The clock signal to be sent to the setting signal input is chosen, for instance, by output selection with the aid of a multipath switch.
One drawback with this solution is that the signal outputs which forward the clock-signal cannot be used with anything other than just clock signals after the the operating mode has been set.